1. Field of the Invention
This invention relates to an insulating powder and compositions suitable for the formation of a resistant coating on a non-oxide ceramic substrate, particularly an aluminum nitride substrate possessing a low thermal expansion coefficient and used for hybrid IC circuit devices.
2. Description of the Prior Art
In recent years, as insulating substrates for hybric IC circuit devices, use of substrates of aluminum nitride, silicon carbide, and silicon nitride in the place of those of alumina has been advocated. In the case of the aluminum nitride substrate, when a resistant coating is formed thereon by applying thereon a composition consisting of an electroconductive powder, glass frit, and an organic vehicle and heretofore used on the conventional alumina substrate, which has been firing the coated substrate, the produced resistant coating lacks stability of quality because the aluminum nitride and the glass react with each other with evolution of a gas. As a solution for this problem, the use in the composition of an insulating powder comprising a crystalline glass frit having as a main ingredient thereof SiO.sub.2, Al.sub.2 O.sub.3, CaO, ZnO, or TiO.sub.2 and not more than 20 parts by weight, used on 100 parts by weight of the glass frit, of at least one member selected from the group consisting of alumina, magnesia, mullite, forsterite, stearite and cordierite has been proposed in Japanese Patent Application Disclosure SHO 62(1987)-21,630.
It is customary to vary the magnitude of resistance to be offered by the produced resistant coating by varying the mixing ratio of the electroconductive powder in the composition prepared for the formation of the resistant coating. Where the glass frit mentioned above is used, an increase in the magnitude of resistance is attained by decreasing the amount of the electroconductive powder and conversely increasing the amount of the glass frit. The amount of glass is increased and the firing temperature is consequently elevated in proportion as the magnitude of resistance increases. Thus, the applied layer of the composition on the substrate, while being fired, is liable to effervesce before the glass is melted and crystallized, rendering it difficult to produce a resistant coating of stable quality.